RFR: 8338426: Test java/nio/channels/Selector/WakeupNow.java failed

[Brian Burkhalter]

`System.currentTimeMillis()` is replaced with `System.nanoTime()` and the elapsed time is added to the failure exception message.

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Commit messages:
 - 8338426: Test java/nio/channels/Selector/WakeupNow.java failed

Changes: https://git.openjdk.org/jdk/pull/21674/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21674&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338426
  Stats: 15 lines in 1 file changed: 4 ins; 2 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/21674.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21674/head:pull/21674

PR: https://git.openjdk.org/jdk/pull/21674